Dragrope fairlead assembly

ABSTRACT

A support member pivotally connects to the front edge of a dragline excavator main frame and a pair of inboard sheaves are mounted thereto for rotation about a first horizontal axis. A pair of sheave blocks, each having a rotatably mounted outer sheave, connect to the support member for rotation about forwardly inclined block pivot axes. A pair of dragropes which connect with a drum on the main frame run beneath the inboard sheaves, up and over the outboard sheaves, and connect with a bucket which is manipulated by the excavator.

United States Learmont tet 1 Octt14, 1975 [54] DRAGROPE FAIRLEAD ASSEMBLY 3,708,152 1/1973 Bolin 254/190 R [75] Inventor: Tom Learmont, Wauwatosa, Wis. P E A" N Kn l rzmary xammeren ow es 1 Asslgneel f c South Assistant Examiner-Larry H. Martin Mllwaukee, Attorney, Agent, or Firm-Quarles & Brady [22] Filed: May 20, 1974 21 App]. No.: 471,246 [57] ABSTRACT Related Application Data A support member pivotally connects to the front C ti mi of Ser No 4 037 Oct 30 5 edge of a dragline excavator main frame and a pair of gg inboard sheaves are mounted thereto for rotation about a first horizontal axis. A pair of sheave blocks,

each having a rotatably mounted outer sheave, conil. 254/190Ii;6,6I:i7/1 met to the pp member for rotation about for [58] Field 125 126 wardly inclined block pivot axes. A pair of dragropes 2 236/1196. 1 which connect with a drum on the main frame run beneath the inboard sheaves, up and over the outboard [56] References Cited sheaves, and connect with a bucket which is manipulated by the excavator. UNITED STATES PATENTS 2,272,917 2/1942 Lawler 254/190 R 12 Claims 6 Drawing Flgures Sheet 1 of 5 US. Patent 0a. 14, 1975 US. Patent Oct. 14, 1975 Sheet 2 of5 3,912,230

US. Patent Oct. 14, 1975 Sheet 3 of5 3,912,239

US. atent Oct. 14, 1975 Sheet 4 of5 3,912,.2

DRAGROPE FAIRLEAD ASSEMBLY This is a continuation of application Ser. No. 41 1,037 filed Oct. 30, 1973, now abandoned.

BACKGROUND OF THE INVENTION The field of the invention is fairlead assemblies for large excavating equipment, and particularly fairlead assemblies for the dragrope on large dragline-type excavators.

In a typical dragline-type excavator, a large bucket is hoisted at the end of a boom; is cast outward; set down on the surface of the ground; and then hauled in or dragged across the surface by means of a dragrope attached to a rotatable drum on the main frame of the excavator. The dragrope is subjected to large forces during this operating cycle, and to reduce the frictional wear on the dragrope as it is cast outward and hauled in, a fairlead assembly is provided along the front edge of the main frame where the dragrope enters the excavator housing. Such fairlead assemblies include sheaves that confine the dragrope and provide rotatable surfaces which guide it to the drum on the main frame. These fairlead assemblies must not themselves introduce excessive wear either by sharply bending the dragrope or by abrading it. On excavators where the dragrope is in the range of three inches in diameter and the fairlead sheaves are eight feet or over in diameter, the size, weight and cost of the fairlead assembly are most important.

SUMMARY OF THE INVENTION The present invention relates to an improved fairlead assembly which includes an inboard sheave rotatably mounted to the excavator mainframe and under which the dragrope passes as it is paid out from a drum, and a rotatably mounted outboard sheave over which the dragrope wraps in its run to a bucket. The outboard sheave is rotatably connected between a pair of cheeks which form a block that is mounted for pivotal motion about a forwardly inclined block pivot axis. The forward sheave is thus free to align itself with the dragrope run between it and the bucket.

A general object of the invention is to minimize the bending in the dragrope which results when the bucket becomes misaligned with respect to the boom. The outboard sheave is free to align with the bucket and the stationary inboard sheave is aligned with the stationary drum. The dragrope thus bends by an amount equal to the misalignment of the two sheaves (commonly referred to in the art as the fleet angle) at the points at which it first contacts the sheaves in its run between them. The inboard and outboard sheaves are oriented with respect to the block pivot axis such that these points of contact, or points of tangency, are equally distant from the block pivot axis. The total bend in the dragrope as it passes between the sheaves is thus divided equally at both points of tangency to thereby minimize the amount of bending and consequent wear on the dragrope at any one point.

Another general object of the invention is to minimize frictional wear on the dragrope by insuring that the dragrope wraps around each sheave at least 30 during all digging conditions. This is accomplished by spacing the sheaves close together on each side of the block pivot axis and raising the upper rope engaging surface of the outboard sheave well above the lower rope engaging surface of the inboard sheave.

Still another object of the invention is to lift the dragrope up off the ground to minimize the amount of dirt brought into the excavator housing. The outboard sheave over which the dragrope wraps is raised well above the ground and the entire fairlead assembly is pivotally mounted to the excavator main frame to allow adjustment of its height to the maximum allowable depending on the type and size of boom attached to the machine.

Another object of the invention is to minimize the overall size and weight of the fairlead assembly. The outboard sheave is mounted between the cheeks of the block and the block is pivotally mounted by upper and lower trunnions. The dragrope passes beneath the inboard sheave, upward and over the outboard sheave through a swallow defined by the cheeks and the upper trunnion. The trunnions are reasonably spaced to minimize the size and weight of the supporting member, and the trunnions are of simple construction.

Still another object of the invention is to damp any swinging motion of the dragrope. The sheave block and associated outboard sheave are pivotally mounted to swing about a forwardly inclined pivot axis and the center of gravity of the sheave block is forward of the pivot axis. As a result, its weight acts to align the outboard sheave with the inboard sheave and to resist, or damp, any swing in the dragrope.

The foregoing and other objects and advantages of the invention will appear from the following description. In the description reference is made to the accompanying drawings which form a part hereof and in which there is shown by way of illustration a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention and reference is made to the claims herein for interpreting the breadth of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view in elevation of a dragline excavator incorporating the fairlead assembly of the present invention;

FIG. 2 is a view in elevation of the invented fairlead assembly;

FIG. 3 is a top view of the invented fairlead assembly;

FIG. 4 is a view taken along the line 44 of the fairlead assembly in FIG. 2;

FIG. 5 is a view in elevation with parts cut away of the invented fairlead assembly; and

FIG. 6 is a view in cross section of the fairlead assembly in FIG. 2 taken along the line 66.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a dragline excavator has a revolving main frame 1 to which a boom 2 is pivotally connected. The boom 2 extends forward and supports a bucket 3 which is raised and lowered by a hoist rope 4. The hoist rope 4 passes over a boom point sheave on the outer end of the boom 2 and connects with a hoist drum 5 mounted on the main frame 1. A pair of dragropes 6 and 6A also connect to the bucket 3 and attach to a power-driven drum 8 mounted on the main frame 1. A housing 7 encloses the machinery and controls (not shown in the drawings) which drive the drums 5 and 8 and which revolve the main frame 1.

Mounted to the foreward edge of the main frame 1 is a fairlead assembly 10 which confines and guides the dragropes 6 and 6A. Referring particularly to FIGS. 2 and 4, the fairlead 10 includes a support member 11 which is formed of steel plates welded together to form a hollow structure that is pivotally mounted to the forward edge of the main frame 1. The pivotal attachment is accomplished at the lower end of the support member 11 by a pair of spaced ears 12 and 13 which are welded to the forward edge of the main frame 1 and which extend forward to each side of the support member 11. Aligned openings in the ears l2 and 13 receive a pin 14 that extends through the support member 11 along a horizontal pivot axis 15. Suitable spacers are disposed between the ears 12 and 13 and the support member 11 to minimize friction and wear.

Referring particularly to FIGS. 2 and 3, a pair of inboard sheaves 16 and 17 are rotatably mounted to each side of the support member 11 at a point well above the top of the main frame 1. A pin 18 extends outward from each side thereof to receive the sheaves 16 and 17. Spacers 22 are disposed between each sheave 16 and 17 and the support member 11 to allow free rotation of the sheaves 16 and 17 about a first horizontal axis of rotation 19 defined by the centerline of the pin 18. The sheaves l6 and 17 are eight feet in diameter and they are positioned such that the dragrope run between the drum 8 and the lower rope engaging surfaces of the inboard sheaves l6 and 17 is substantially horizontal.

In addition to supporting the sheaves l6 and 17, the pin 18 also serves as a connection point for one end of an adjusting link 20. An opening in the rear surface of the support member 11 exposes the mid portion of the pin 18, and one end of the adjusting link 20 connects thereto. The other end of the link 20 is connected to the main frame 1 by means of a pin 21 which passes through an opening therein and through aligned openings in a pair of ears 22 and 23. The ears 22 and 23 connect to and extend upward from the deck of the main frame 1. Although the link 20 is fixed in length in any one application, a selection of lengths are provided to accompany the various types and sizes of available booms. For example, a long link 20 pivots the support member 11 forward about the pivot axis to increase the clearance between the fairlead assembly 10 and the bottom of the boom 2 which passes immediately above. On the other hand, the attachment of a shorter link is possible where smaller booms are used and there is substantial clearance above the fairlead assembly 10. This is desirable because the further the dragropes are lifted off the ground the less the amount of dirt which they pick up and bring into the machinery housing 7.

Referring to FIGS. 2-6, the support member 11 also mounts a pair of sheave blocks 27 and 28. The sheave block 27 is supported by an outward extending pedestal portion 25 which is formed to the support member 11 by weldments attached near its lower end. The block 27 is retained by a top 26 which is fastened to the top of the support member 11 by bolts 24 and which includes a pair of forwardly and outwardly extending cap portions 39 and 40. The sheave block 27 includes a pair of spaced, upright cheeks 62 and 63 formed from steel plates and joined at their upper and lower ends by upper and lower trunnions 29 and 30, respectively. The upper trunnion 29 extends upward and is received in an opening in the cap portion 29 and is rotatably maintained therein by a bushing 31. Similarly, the lower trunnion 30 extends downward into an opening in the pedestal 25 and is rotatably retained therein by a bushing 32. The upper and lower trunnions 29 and 30 define a first block pivot axis 33 about which the sheave block 27 pivots, or swings. The axis 33 is forwardly inclined and is in the plane of the inboard sheave 16.

The sheave block 28 is similarly constructed and it includes a pair of cheeks 34 and 35 which are connected by upper and lower trunnions 36 and 37. The sheave block 28 is pivotally mounted between a pedestal 22 and the cap portion 40 to swing about a second pivot axis 38 which is parallel to the first pivot axis 33 and is in the plane of the second inboard sheave 17.

Referring particularly to FIGS. 2 and 3, the sheave blocks 27 and 28 each mount an outboard sheave 41 and 42, respectively. The sheaves 41 and 42 are identical to the inboard sheaves 16 and 17 and are rotatably mounted to the blocks 27 and 28 for rotation in the planes of the respective inboard sheaves 16 and 17 when the sheave blocks are straight, or aligned. More specifically, the outboard sheave 41 is mounted between the cheeks 62 and 63 of the block 27 by a pin 43 which extends through a central opening in the sheave 41 and into annular shaped hubs 44 and 45 formed on the cheeks 62 and 63. Similarly, the outboard sheave 42 is rotatably mounted between the cheeks 34 and 35 by a pin 46 which extends through a central opening in the sheave 42 and into hubs 47 and 48. The pins 43 and 45 define a second horizontal axis of rotation 49 that is parallel to the first horizontal axis of rotation 19 when the outboard sheaves 41 and 42 are in their aligned position. It should be apparent, however, that when the sheave blocks 27 and 28 swing to either side, as shown, for example, in FIG. 3, the axes of rotation of the outboard sheaves 41 and 42 swing away from the second horizontal axis of rotation 49 a corresponding amount.

As shown best in FIGS. 2-4, the sheave blocks 27 and 28 are free to pivot about the respective block pivot axes 33 and 38. Such misalignment occurs, for example, when the bucket 3 swings to one side or the other of the boom 2 at various times during the digging cycle, or when the dragropes themselves begin to swing back and forth to either side of the boom 2. To inhibit the extent of such a swinging motion the sheave blocks 27 and 28 are tied together by a chain 52 which connects between the cheeks 28 and 34. Although some slack is provided in the chain 52 to allow a slight relative pivotal motion of the sheave blocks 27 and 28, it serves to maintain them in essentially parallel planes at all times. A limit wire 53 connects to the sheave block 28 and extends outboard to connect with the main frame 1. Similarly, a limit wire 54 connects the sheave block 27 to the main frame 1 at a point on the opposite side of the fairlead assembly 10. One end of the wire 53 connects through a swivel connector 55 to the main frame 1 and the other end connects through a swivel connector 56 to a pair of cars 57 which are integrally formed on the check 35. Similarly, the limit wire 54 connects to the main frame 1 and to a pair of ears 59 through a swivel 58. The wires 53 and 54 limit the extent to which the sheave blocks 27 and 28 can swing about their axes 33 and 38.

The bucket 3 rarely becomes misaligned with respect to the boom 2 more than a few degrees under normal operating conditions. Any further misalignment of the dragropes 6 and 6A is, therefore, usually due to the dragropes swinging. It is one of the general objects of the present invention that such'swinging motions be damped and it should be apparent that the limit wires 53 and 54 in association with the chain 52 aid in this endeavor. In addition, however, the center of gravity of each sheave block and associated outboard sheave is well forward of its inclined block pivot axis. As a result, the weight of each sheave block and sheave acts to maintain the sheave block in alignment and to resist forces which tend to misalign it. The greater the forward inclination of the block pivot axes 33 and 38, the greater the damping force generated to retard swinging motions in the dragropes 6 and 6A.

Referring particularly to FIG. 5, the dragrope 6 runs from the drum 8 on the main frame 1 beneath the inboard sheave 16, up and over the outboard sheave 41 and to the bucket 3. The dragrope 6 runs between the cheeks 62 and 63, through a swallow defined by the sheave block 27 and the upper rope engaging surface of the outboard sheave 41. The dragrope 6A is similarly strung through the sheaves 17 and 42. It has been discovered that at least and preferably 30, of engagement is required to prevent the sheaves 16-and 41 from rotating with respect to the dragrope 6 during all phases of the digging operation. For example, when the bucket 3 is cast outward, the dragrope 6 is paid out rapidly and the sheaves 16 and 41 develop considerable angular momentum. When the payout of the dragrope 6 is suddenly stopped, the engagement between it and the sheaves 16 and 41 must be substantial if the sheaves are also to be brought to a rapid stop without abrading the dragrope 6. The relative positions of the horizontal axes of rotation 19 and 49 in the preferred embodiment of the invention are such that the rope'6 engages the lower rope engaging surface of the inboard sheave l6 and wraps around approximately 50 of its circumference- Similarly, the rope 6 engages the upper rope engaging surface of the outboard sheave 41 and wraps around at least 50 of its circumference during all portions of the digging cycle. Substantial engagement between the rope 6 and the sheave 16 and 41 is thus established to insure that the rope 6 is not abraded, or overheated, by relative motion between it and the sheaves.

It is another teaching of the present invention that the horizontal axes of rotation 19 and 49 should be properly positioned with respect to the block pivot axis 33. More specifically, as the dragrope 6 disengages from the inboard sheave 16 at a point of tangency indicated by the arrow 60 it will bend out of the plane of the inboard sheave 16 when the outboard sheave 41 is misaligned. Similarly, as the dragrope 6 first engages the outboard sheave 41 at the point of tangency indicated by the arrow 61, it will bend into the plane of the outboard sheave 41. The total bend at the points of tangency 60 and 61 is equal to the fleet angle which in turn is linearly related to the amount which the outboard sheave 41 is misaligned with inboard sheave 16. The amount of bending which occurs at either point of tangency 60 and 61 can be minimized to a certain extent by dividing the total bend equally between the two points. This is accomplished by positioning the sheaves 16 and 41 such that their respective points of tangency 60 and 61 are equally spaced from the block pivot axis 33. Also, the amount of bending is further minimized by locating the points of tangency 60 and 61 as close as possible to the block pivot axis 33. In fact, it can be appreciated that if the points of tangency 60 and 61 are on the block pivot axis 33, no bending occurs, but instead, the dragrope 6 is merely twisted by an amount equal to the fleet angle. Although bending can thus be eliminated if the dragrope run between the points of tangency and 61 coincides with the block pivot axis 33, in practice, this requires that the trunnions 29 and 30 be excessively spaced apart, or that the lower trunnion 30 have a coaxial opening through which the dragrope 6 may pass. The increased cost, size and weight which either of these structures requires is prohibitive when applied to fairlead assemblies of the size required in dragline excavators. It is a teaching of the present invention, therefore, that the points of tangency 60 and 61 should be maintained as close as possible to the block pivot axis 33 and that they should be spaced equal distances to either side of the block pivot axis 33.

A new and improved fairlead assembly for use on large dragline excavators has been described and is believed to solve many of the long standing problems associated with this art. It should be apparent that many variations can be made to the specific structure described herein without departing from the spirit of the invention, and reference is therefore made to the following claims for a definition of the invention.

1 claim:

1. In an excavating machine having a boom which supports a bucket on the end of a hoist rope and which is connected to extend forward from a main frame, and having a dragrope which runs from the bucket to a power driven drum mounted on the main frame, a fairlead assembly for guiding the dragrope in its run between the bucket and the power driven drum, the combination comprising:

a support member pivotally attached at its lower end to the forward edge of said main frame to swing about a horizontal pivot axis;

an adjusting link connected to said support member and to said main frame to lock said support member in a fixed position;

an inboard sheave rotatably mounted to said support member for rotation about a first horizontal axis of rotation;

a sheave block mounted to said support member for swinging motion about a forwardly inclined block pivot axis which is forward of and in the plane of saidinboard sheave, said sheave block including a pair of spaced upright cheeks;

and an outboard sheave rotatably mounted to said sheave block between said cheeks for rotation about a second horizontal axis of rotation;

wherein said dragrope runs from said power driven drum beneath said inboard sheave to wrap around a lower rope engaging surface on said inboard sheave, and extends upward through a swallow defined by said sheave block cheeks and over said outboard sheave to wrap around an upper rope engaging surface on said outboard sheave.

2. The fairlead assembly as recited in claim 1 in which the upper rope engaging surface of said outboard sheave is substantially above the lower rope engaging surface of said inboard sheave and said dragrope wraps around at least 20 of circumference of each of said inboard and outboard sheaves.

3. The fairlead assembly as recited in claim 2 in which said sheave block includes upper and lower trun nions which are coaxial with said block pivot axis and which are received in openings in said support member to trunnion mount said sheave block.

4. The fairlead assembly as recited in claim 2 in which the points of tangency which define each end of the dragrope run between sheaves are on opposite sides of said block pivot axis and are equally spaced therefrom.

5. The fairlead assembly as recited in claim 4 in which said sheave block is mounted to said supporting member by an upper trunnion which is coaxial with said block pivot axis and disposed above said points of tangency, and a lower trunnion which is coaxial with said block pivot axis and disposed below said points of tangency.

6. The fairlead assembly as recited in claim 1 in which a second inboard sheave is attached to said support member for rotation about said first horizontal axis of rotation, a second sheave block is mounted to support member for swinging motion about a second block pivot axis which is in the plane of said second inboard sheave and parallel to said first block pivot axis, a second outboard sheave is rotatably mounted to said second sheave block, and a second dragrope runs beneath said second inboard sheave and over said second outboard sheave.

7. In an excavating machine having a boom which supports a bucket on the end of a hoist rope and which is connected to extend forward from a main frame, and having a dragrope which runs from the bucket to a power driven drum mounted on the main frame, a fairlead assembly for guiding the dragrope in its run between the bucket and the power driven drum, the combination comprising:

a support member attached to the forward edge of said main frame;

an inboard sheave rotatably mounted to said support member for rotation about a first horizontal axis of rotation;

a sheave block mounted to said support member for swinging motion about a forwardly inclined block pivot axis which is forward of and in the plane of said inboard sheave; and

an outboard sheave rotatably mounted to said sheave which said sheave block includes upper and lower trunnions which are coaxial with said block pivot axis and which are spaced apart along said block pivot axis to allow said dragrope to pass therebetween in its run between the inboard and outboard sheaves.

9. The fairlead assembly as recited in claim 7 in which the points of tangency which define each end of the dragrope run between the inboard and outboard sheaves are on opposite sides of said block pivot axis and are equally spaced therefrom.

10. The fairlead assembly as recited in claim 7 in which the upper rope engaging surface of said outboard sheave is substantially above the lower rope engaging surface of said inboard sheave and said dragrope wraps around at least 20 of circumference of each of said inboard and outboard sheaves.

11. In an excavating machine having a boom which supports a bucket on the end of a hoist rope and which is connected to extend forward from a main frame, and having a dragrope which runs from the bucket to a power driven drum mounted on the main frame, a fairlead assembly for guiding the dragrope in its run between the bucket and the power driven drum, the combination comprising:

an inboard sheave rotatably mounted to said main frame for rotation about a first horizontal axis of rotation;

a sheave block mounted to said main frame for swinging motion about a forwardly inclined block pivot axis which is forward of and in the plane of said inboard sheave; and

an outboard sheave rotatably mounted to said sheave block for rotation about a second horizontal axis of rotation;

wherein said dragrope runs from said power driven drum beneath said inboard sheave to wrap around a lower rope engaging surface on said inboard sheave, and extends upward and over said outboard sheave to wrap around an upper rope engaging surface on said outboard sheave.

12. The fairlead assembly as recited in claim 11 in which said sheave block includes upper and lower trunnions which are coaxial with said block pivot axis and which are spaced apart along said block pivot axis to allow said dragrope to pass therebetween in its run between the inboard and outboard sheaves, and in which the points of tangency which define each end of the dragrope run between the inboard and outboard sheaves are on opposite sides of said block pivot axis and are equally spaced therefrom. 

1. In an excavating machine having a boom which supports a bucket on the end of a hoist rope and which is connected to extend forward from a main frame, and having a dragrope which runs from the bucket to a power driven drum mounted on the main frame, a fairlead assembly for guiding the dragrope in its run between the bucket and the power driven drum, the combination comprising: a support member pivotally attached at its lower end to the forward edge of said main frame to swing about a horizontal pivot axis; an adjusting link connecTed to said support member and to said main frame to lock said support member in a fixed position; an inboard sheave rotatably mounted to said support member for rotation about a first horizontal axis of rotation; a sheave block mounted to said support member for swinging motion about a forwardly inclined block pivot axis which is forward of and in the plane of said inboard sheave, said sheave block including a pair of spaced upright cheeks; and an outboard sheave rotatably mounted to said sheave block between said cheeks for rotation about a second horizontal axis of rotation; wherein said dragrope runs from said power driven drum beneath said inboard sheave to wrap around a lower rope engaging surface on said inboard sheave, and extends upward through a swallow defined by said sheave block cheeks and over said outboard sheave to wrap around an upper rope engaging surface on said outboard sheave.
 2. The fairlead assembly as recited in claim 1 in which the upper rope engaging surface of said outboard sheave is substantially above the lower rope engaging surface of said inboard sheave and said dragrope wraps around at least 20* of circumference of each of said inboard and outboard sheaves.
 3. The fairlead assembly as recited in claim 2 in which said sheave block includes upper and lower trunnions which are coaxial with said block pivot axis and which are received in openings in said support member to trunnion mount said sheave block.
 4. The fairlead assembly as recited in claim 2 in which the points of tangency which define each end of the dragrope run between sheaves are on opposite sides of said block pivot axis and are equally spaced therefrom.
 5. The fairlead assembly as recited in claim 4 in which said sheave block is mounted to said supporting member by an upper trunnion which is coaxial with said block pivot axis and disposed above said points of tangency, and a lower trunnion which is coaxial with said block pivot axis and disposed below said points of tangency.
 6. The fairlead assembly as recited in claim 1 in which a second inboard sheave is attached to said support member for rotation about said first horizontal axis of rotation, a second sheave block is mounted to support member for swinging motion about a second block pivot axis which is in the plane of said second inboard sheave and parallel to said first block pivot axis, a second outboard sheave is rotatably mounted to said second sheave block, and a second dragrope runs beneath said second inboard sheave and over said second outboard sheave.
 7. In an excavating machine having a boom which supports a bucket on the end of a hoist rope and which is connected to extend forward from a main frame, and having a dragrope which runs from the bucket to a power driven drum mounted on the main frame, a fairlead assembly for guiding the dragrope in its run between the bucket and the power driven drum, the combination comprising: a support member attached to the forward edge of said main frame; an inboard sheave rotatably mounted to said support member for rotation about a first horizontal axis of rotation; a sheave block mounted to said support member for swinging motion about a forwardly inclined block pivot axis which is forward of and in the plane of said inboard sheave; and an outboard sheave rotatably mounted to said sheave block for rotation about a second horizontal axis of rotation; wherein said dragrope runs from said power driven drum beneath said inboard sheave to wrap around a lower rope engaging surface on said inboard sheave, and extends upward and over said outboard sheave to wrap around an upper rope engaging surface on said outboard sheave.
 8. The fairlead assembly as recited in claim 7 in which said sheave block includes upper and lower trunnions which are coaxial with said block pivot axis and which are spaced apart along said block pivot axis to allow said dragrope to pass therebetween in its run between the inboard and outboard sheaVes.
 9. The fairlead assembly as recited in claim 7 in which the points of tangency which define each end of the dragrope run between the inboard and outboard sheaves are on opposite sides of said block pivot axis and are equally spaced therefrom.
 10. The fairlead assembly as recited in claim 7 in which the upper rope engaging surface of said outboard sheave is substantially above the lower rope engaging surface of said inboard sheave and said dragrope wraps around at least 20* of circumference of each of said inboard and outboard sheaves.
 11. In an excavating machine having a boom which supports a bucket on the end of a hoist rope and which is connected to extend forward from a main frame, and having a dragrope which runs from the bucket to a power driven drum mounted on the main frame, a fairlead assembly for guiding the dragrope in its run between the bucket and the power driven drum, the combination comprising: an inboard sheave rotatably mounted to said main frame for rotation about a first horizontal axis of rotation; a sheave block mounted to said main frame for swinging motion about a forwardly inclined block pivot axis which is forward of and in the plane of said inboard sheave; and an outboard sheave rotatably mounted to said sheave block for rotation about a second horizontal axis of rotation; wherein said dragrope runs from said power driven drum beneath said inboard sheave to wrap around a lower rope engaging surface on said inboard sheave, and extends upward and over said outboard sheave to wrap around an upper rope engaging surface on said outboard sheave.
 12. The fairlead assembly as recited in claim 11 in which said sheave block includes upper and lower trunnions which are coaxial with said block pivot axis and which are spaced apart along said block pivot axis to allow said dragrope to pass therebetween in its run between the inboard and outboard sheaves, and in which the points of tangency which define each end of the dragrope run between the inboard and outboard sheaves are on opposite sides of said block pivot axis and are equally spaced therefrom. 